The present invention relates to a hydraulic elevator and more particularly to a hydraulic elevator provided with a control device for correcting undesired effects on the running speed characteristic due to variation in temperature of operating oil, in load, etc.
A hydraulic elevator of the type in which speed control is performed by controlling the flow of pressure-oil supplied to or discharged from a hydraulic cylinder is known from, for example, U.S. Pat. No. 3,955,649 issued on May 11, 1976 and entitled "Device for Correcting Floor Level of Hydraulic Elevator".
In the hydraulic elevator of this type, the cage-speed control has been performed by hydraulically or mechanically actuating flow control valves in suitable sequence.
In such a control, however, the speed in acceleration, deceleration, full-running, landing or the like, may vary due to variation in oil temperature and/or load. Accordingly, the time through which a cage runs at the landing speed is prolonged, so that not only excessive power is required but also passengers may feel uncomfortable.
One approach to shorten the landing-speed running time is to delay the timing of generating a cage-deceleration instruction. In this approach, however, since the delay times in operation of various flow control valves for deceleration are fixed to predetermined values in spite of possible variations in operation characteristics of the respective flow control valves due to manufacturing and/or adjusting errors thereof, there are problems in providing a comfortable ride for passengers in that the landing-speed running time is not always constant and an error in landing may occur, even if the landing-speed running time can be shortened.